In recent, because of excellent characteristics of a gallium nitride (GaN) semiconductor, a nitride semiconductor LED is widely studied.
Specifically, in order to use the nitride LED for illumination as well as for display, the brightness limit of the commercialized LED should be overcome.
The nitride LED generally emits light in an element area having a diameter of 300 μm or more. The light emitted from a luminous layer may not get out of the element and be locked in the element, so that the nitride LED has a limit that its external luminous efficiency does not exceed 30%.
In order to solve this problem, the internal luminous efficiency and the external luminous efficiency should be optimized, respectively. Since most GaN is grown using a heterogeneous epitaxy technology, a plurality of lattice defects necessarily exist therein, thereby resulting in deterioration of the internal luminous efficiency.
Nonetheless, the recent GaN growth technologies have a tendency to be based on the heterogeneous epitaxy technology, and thus it is difficult to expect enhancement of the internal luminous efficiency any more. Therefore, trials for enhancing the luminous efficiency through technologies such as efficient formation of electrodes and packaging technologies of enhancing concentration of light with an element structure previously optimized and grown into a thin film have been issued.